Semiconductor switching devices of a power converter, such as an inverter, perform switching operations based on drive signals which undergo pulse width modulation (PWM) where the carrier frequency is in the range of about several KHz to about twenty KHz. Due to these switching operations, switching noises having frequency components of several dozens of KHz are generated from the power converter.
Since frequency components of the switching noises that are greater than one hundred KHz have adverse influences on external equipment, various legal regulations have been laid on power converters in recent years, in an attempt to reduce or eliminate such adverse influences. To deal with these regulations, noise-cut filters are installed on the power converters.
A known example of noise-cut filter for a power converter includes a single reactor formed by winding an electric wire around a core, such as of ferrite, amorphous alloy or crystalline alloy, and a single condenser in the form of a film or a chip. The reactor and the condenser are coupled into an inverted L-shape, to thus provide a filter for filtering switching noises that occur upon switching operations of semiconductor switching devices of the power converter.
The reactor used in this known type of noise-cut filter generally has a toroidal shape, and the condenser is a pin-inserted type and has a flat shape or a cylindrical shape. Where these reactor and condenser are mounted on a printed board within the power converter, space required for mounting will be greater than the sum of volumes of individual elements. Further, mounting of such filters with separate wiring results in an undesirably large number of coupling portions, and a complicated manner of fixing individual components.
Commercially available so-called composite LC filters of a chip type or pin-inserted type, in which an inductor and a condenser are integrated, have a cut-off frequency of several MHz or higher, whereas the cut-off frequency normally needed to filter switching noises occurring upon switching operations of semiconductor switching devices is as low as about 150 KHz, for example. Further, in a power converter such as an inverter, several amperes of current is required to flow through the commercially available filter. Thus, it has been difficult to employ the commercially available, low-cost composite LC filter for use in the power converter.